US special forces captured a top chemical weapons engineer working for Islamic State during a raid last month in northern Iraq, officials said on Wednesday, dealing a blow to the militants’ pursuit of what Pentagon officials call “weapons of mass destruction”.

Sleiman Daoud al-Afari was snatched close to a month ago in the town of Badoosh, north-west of the Isis stronghold of Mosul. A senior Iraqi official said he was an industrial engineer in former dictator Saddam Hussein’s military and had been a member of Isis throughout all its earlier incarnations.

Isis is believed to have used mustard gas at least twice against Kurdish forces in northern Iraq, and once against anti-Assad rebels in northern Syria. The latter attack killed a four-year-old girl in the village of Merae, near the Turkish border. It was launched as Isis tried to move towards the Syrian border town of Azaz. At least six other residents of the village were hospitalized in Turkey after the attack, several with giant weeping blisters across their body.

It was also reported on Wednesday that more than 40 people suffered partial choking and skin irritation in northern Iraq on Tuesday when Isis fired mortar shells and Katyusha rockets filled with “poisonous substances” into their village.

Afari is reportedly in his 50s. Hisham al-Hashimi, an Iraqi author and academic, said: “He is the technical expert on the chemical weapons project, but Taha Rahim al-Dulaimi is the ideological driver of this. He is an important figure within the organization.”

The prospect of Isis gaining large scale chemical weapons would raise the stakes significantly in Iraq, where a chemical attack on the Kurdish village of Halabja by Saddam’s forces in 1988 left thousands of people dead. The extremist group is believed to have set up a special unit for chemical weapons research, made up of Iraqi scientists from the Saddam-era weapons programme along with foreign experts.

Jeff Davis, a spokesman for the Pentagon, declined to confirm that an individual had been captured but noted: “We’ve said before that they have used chemical weapons in both Iraq and Syria: sulphur mustard specifically. Anyone who’s making and using weapons of mass destruction, particularly a terrorist group such as Isis, would be well advised to know that we don’t intend to let them keep doing that.”

Iraqi and US officials claimed Afari’s capture as the first known major success of a new strategy to deploy a commando unit to Iraq dedicated to capturing and killing Isis leaders in clandestine operations. Little is known about it, but defense secretary Ash Carter told a Senate hearing in December: “This is a no-kidding force that will be doing important things.”

The operation that captured Afari in late February did not result in casualties, according to a US official. Afari is held in a temporary US detention facility in Iraq ahead of an unscheduled transfer to Iraqi authorities.

The US-led coalition began targeting Isis’s chemical weapons infrastructure with airstrikes and special operations raids over the past two months, Iraqi intelligence officials and a western security official in Baghdad told the Associated Press. Airstrikes are targeting laboratories and equipment, and further special forces raids targeting chemical weapons experts are planned, the intelligence officials said.

Khaled al-Obaidi, the Iraqi defence minister, insisted that Isis, which seized swathes of territory in northern and western Iraq in 2014, lacks “chemical capabilities”. He told reporters at a base outside Tikrit that attacks carried out by the group are only intended to “hurt the morale of our fighters”, since they have not yet caused any casualties.

But reports on Wednesday said a village in northern Iraq had become the latest target of a chemical attack. None of the 40 casualties died but five of them remain in hospital, health officials in Taza, a mainly Shia Turkmen village 12 miles south of Kirkuk, told Reuters.

Kirkuk province governor Najmuddin Kareem was quoted as saying: “There were poisonous substances in these shells. We don’t know what.”

Using an alternative name for Isis, he added: “Daesh wants to scare off the population. They want to show they have chemical weapons just like the previous regime.”

A total of 24 shells and rockets were fired into Taza from the nearby Bashir area, added Wasta Rasul, a commander of the Kurdish peshmerga forces in the region.

Josh Earnest, the White House press secretary, said: “At this point, there has been some evidence and some discussion and even some reports about potential use of chemical weapons by Isil. We’re reviewing those reports.

“Obviously the use of chemical weapons by anybody is an atrocity and one that the international community will not stand for. However, if those reports are correct, it would not be an outlier in terms of the tactics that we know that Isil uses. We know that Isil is an extremist organisation that seeks to achieve their aims by terrorising innocent people.”

The US has been leading a coalition waging airstrikes against Isis in Iraq and Syria for more than a year. The campaign is working to support Iraqi and Kurdish forces that have slowly retaken significant parts of territory the militants had seized.

But on Wednesday, General Joseph Votel, the current commander of US Special Operations Command and tapped to lead US Central Command, told a Senate panel that he has concerns about progress against Isis in Syria. Throughout his confirmation hearing, Votel indicated he would take a more aggressive approach to the Middle East and South Asia than his cautious predecessor, General Lloyd Austin.

Votel said he would conduct a strategy review on Syria, to see if the US had “the coherence that is required, that we have the resources we need … and that we have the authorities,” suggesting an increase of troops or equipment could be a feature of his almost certain tenure at Central Command.

Votel indicated that ousting Isis from the Iraqi city of Mosul and its Syrian capitol of Raqqa “will take additional resources.” Carter, the US defense secretary, has set the recapture of both cities as a critical goal for the war in 2016, a mission met with much scepticism surrounding its feasibility.